1. Field of the Invention
The present invention relates to a variable capacity wobble plate type refrigerant compressor, and more particularly, to a rotation sensing system enabling an accurate detection of a rotation of the internal compressing mechanism of the variable capacity wobble plate type refrigerant compressor.
2. Description of the Related Art
The variable capacity wobble plate type refrigerant compressor includes a cylinder block, an open-ended rear housing having suction and discharge chambers therein and connected to an end of the cylinder block, an open-ended crankcase having a crank chamber therein and connected to the other end of the cylinder block, an axial drive shaft extending through the crankcase and the cylinder block to be rotatable about a longitudinal axis thereof, a reciprocatory piston mechanism provided in the cylinder block for carrying out a pumping-in of a refrigerant gas before compression, a compression of the refrigerant gas, and a delivery of the compressed refrigerant gas, and an assembly of a non-rotatable wobble plate and a rotatable drive plate arranged in the crank chamber for reciprocating the pistons of the piston mechanism via piston rods in response to a rotation of the drive plate. The assembly of the non-rotatable wobble plate and rotatable drive plate is supported on a support element fixedly mounted on the drive shaft and rotated therewith.
The support element mounted on the drive shaft is formed as a generally circular element having a circular base portion, and is supported by an inner wall of the crankcase via a thrust bearing having a pair of axially confronting race members enabling a plurality of roller members to rotate therebetween. The base portion of the support element is provided with a central bored boss by which the element is mounted on the drive shaft, a radially projected arm to which the drive plate is pivotably connected via a pivoting pin, and a partial rim portion allowing the drive plate to perform a dynamically balanced rotation and wobbling when driven by the drive shaft. The partial rim of the support element is circularly extended around a part of the base portion, and is provided with a diameter larger than that of the base portion.
The variable capacity wobble plate type refrigerant compressor is further provided with an electro-magnetic induction type rotation detector for detecting a rotation of internal elements of the compressor, i.e., the support element, and the assembly of the drive and wobble plates. A typical rotation detector for a refrigerant compressor having a swash plate type conversion mechanism for converting a rotation of a drive shaft into a reciprocatory compressing motion of pistons is disclosed in e.g., U.S. Pat. No. 4,462,491 to Kono et al. The rotation detector of U.S. Pat. No. 4,462,491 includes an electromagnetic induction type sensing element having a bar magnet, and an electric coil enclosing the bar magnet and generating an electric signal in cooperation with a rotating sensed element.
The other conventional rotation detector for a wobble plate type compressor includes a mechanical projection formed in one of the above-mentioned metallic race members of the thrust bearing, i.e., the race member fixed to the support element, and a stationary sensing element generating a detecting signal when electromagnetically sensing the projection rotated with the support element. The projection of the race member is arranged at a position on the borders of the smaller base portion and the larger partial rim portion of the support element to generate an electric signal at each complete revolution of the support element. The projection is bent at about a right angle in such a manner that a bent portion thereof is radially located outside the outer circumference of the base portion of the support element, to function as a sensed portion electromagnetically cooperating with the stationary sensing element to thereby produce the detecting signal in the form of an electric voltage signal indicating that the internal elements of the compressor are actually rotated.
The wave form of the electric voltage signal of the rotation detector shows plus and minus different polarities in response to a change in the positional relationship between the sensed portion of the projection and the stationary sensing element, i.e., a movement of the sensed portion approaching an exact opposing position where it is in registration with the stationary sensing element, and the other movement of the sensed portion moving away from the exact opposing position, produce a change in the polarity of the electric voltage signal of the sensing element. Also, the absolute values of the electric voltage signal are greatly different from one another when the polarity of the signal is different. Namely, during the rotation of the support element, when the sensed portion of the projection, preceded by a portion of the outer circumference of the smaller base portion of the element, passes the stationary sensing element, the electric voltage signal exerted by the sensing element has a large absolute value. Nevertheless, during the rotation of the support element, when a portion of the outer circumference of the larger rim portion of the element, preceded by the sensed portion of the projection, passes the sensing element, the absolute value of the electric voltage signal become small. Therefore, the wave form of the electric voltage signal of the rotation detector of the conventional wobble plate type refrigerant compressor is not symmetrical to a reference level, i.e., a zero voltage level, and accordingly, such an asymmetry of the electric voltage signal of the rotation detector makes it difficult to establish a proper reference level of the signal during the electronic processing thereof in the later stage of determining whether or not the internal element in the compressor is actually rotated. As a result, it is impossible to expect an accurate detection of the rotation by the rotation detector of the conventional compressor. In this connection, one method of solving the asymmetry problem of the rotation detecting signal can be taken in which the sensed portion of the projection is shifted radially outward with respect to the outer circumference of the larger rim portion of the support element, so that an approximately equal electro-magnetic induction principle appears on both sides of the sensed portion of the projection in relation to the sensing element. Nevertheless, the method of shifting the projection outward causes a problem of an increase of an outer diameter of the compressor per se.